It is known in fact that solar cells incorporate this type of conductive substrate, which is then coated with a layer of absorbent, generally made of a chalcopyrite based on copper Cu, indium In and selenium Se and/or sulfur S. It may, for example be a material of the CulnSe2 type. This type of material is known by the abbreviation CIS.
For this type of application, the electrodes are usually based on molybdenum Mo, as this material has a number of advantages: it is a good electrical conductor (relatively low specific resistance of about 5.2 mW·cm); it may be subjected to the necessary high heat treatments, as it has a high melting point (2,610° C.); and it exhibits good resistance, to a certain extent, to selenium and to sulfur. The deposition of the absorbent layer usually means that there must be contact with an atmosphere containing selenium or sulfur, which tends to cause most metals to deteriorate. In contrast, molybdenum reacts on the surface with selenium especially, forming MoSe2. However, it keeps most of its properties, especially electrical properties, and maintains a suitable electrical contact with the CIS layer. Finally, molybdenum is a material which adheres well to the CIS layers—it even tends to promote their crystalline growth thereof.
However, it has a major drawback when considering industrial production—it is an expensive material. This is because the Mo layers are usually deposited by sputtering (enhanced by a magnetic field). Now, Mo targets are expensive. This is all the less negligible as, in order to obtain the desired level of electrical conductivity (a resistance per square of less than 2, and preferably less than 1 or 0.5 ohms:square Ω□ after treatment in an atmosphere containing S or Se), a thick Mo layer, generally of about 700 nm to 1 micrometer, is required.